On September 1st, 1983, Korean Air Lines Flight 007 was making a regularly scheduled flight
from New York to Seoul, South Korea via Anchorage.
Unknown to the pilots, because of an error in setting the autopilot system, the plane
began deviating from its intended course, and flew over Russian controlled airspace
in Kamchatka.
Today, this deviation would have been easily noticeable on the flight computer’s GPS
system.
GPS had been invented a decade earlier, but up until this point, it remained a tightly
guarded asset of the US military, and wasn’t shared with commercial pilots.
The autopilot systems of the time followed magnetic courses based on the Earth’s electromagnetic
field.
So far out into the Pacific, away from the ground-based radar stations in Seoul, these
magnetic courses would have been the pilot’s main navigational guide.
The Russians, thinking flight 007 was an American reconnaissance plan, ordered the planes shot
down.
All 269 souls aboard, including a US Congressman, died.
Amidst the national outlash, President Ronald Reagan gave civilian access to the Global
Positioning System to prevent future accidents like these from ever occurring again.
But this paints an interesting question.
If GPS became available to pilots in 1983, how did planes traverse the globe in the seventy
years prior.
Be sure to let us know what you think of the video down in the comments down below (it’s
really helpful for small us channels), and let’s jump in.
*intro*
Early planes of the 1910’s usually had less than 20 passengers or a few bags of mail.
They only flew during the day at a cruising altitude under 3,000 feet and only around
100 mph.
At these lower speeds and altitudes, early pilots used a system known as pilotage, literally
using points of reference on the ground, like mountains or lakes, to determine their position
and their desired course.
Going into the 1920’s, pilots began flying further, more often, and overnight.
As a result, pilots expanded the navigational tools they had at their disposal.
At night, it would be impossible to fly by pilotage, since a pilot couldn't see any landmarks.
Instead, these early pilots would follow the stars and fly by celestial navigation.
Using a tool called a bubble sextant, aircrew looked through an eyepiece and aligned the
sextant’s crosshairs with a known star measuring its angle above the horizon.
They would take several measurements, and comparing these values to a log book of the
stars, determine their position in the sky.
Big errors were common due to things like reading incorrect angles at night, turbulence
from a bumpy plane, or shooting the wrong star.
After all, on a dark night over the Pacific, there would be literal millions of stars.
Over the oceans, they also used a tool called a drift sight; a periscope extending from
the bottom of a plane.
Flying over the ocean, aircrew could look through the drift sight at the waves moving
below and calculate the wind speed and direction using simple geometry.
The aircraft heading could then be adjusted left or right to keep the plane on the proper
course.
But the drift sight was only useful at low altitudes during daytime flights.
Another early technique of the 1910’s was dead reckoning.
Dead reckoning was a method of navigation by estimating your current position by using
a previously determined position and projecting out your current position based on airspeed,
elapsed flight time, and heading.
As you can imagine, the errors from this compound the further out you try to project, but during
daytime flights when you couldn’t see the stars and if you there weren’t any identifiable
landmarks (like if you’re flying over a forest or ocean) this method of guestimation
was the best thing the pilots could do.
Charles Lindbergh used dead reckoning on his famous non-stop solo flight from the United
States to Paris.
And there were some more creative navigational schemes before the invention of radio positioning.
In the later part of the 1920s, the US government set up a series of navigational guides across
the US.
Giant, cartoon-style arrows, stretching in an illuminated path on the ground from New
York to San Francisco.
This rudimentary form of navigation was part of the Transcontinental Airway System, an
effective aid for air-mail pilots that by the '30s incorporated 1,500 ground beacons
over some 18,000 miles.
Every 10 miles, pilots would pass a bright yellow 70-foot concrete arrow on the ground
with a 50-foot rotating beacon in the center.
The arrows were accompanied with pairs of lights that would flash a code, identifying
the beacon's number and thus telling pilots how far they were along the course.
The arrows represented a leap forward from previous attempts at lighted guideposts.
One of which involved setting huge bonfires next to landing strips to help guide pilots
in the night.
In the early 30’s the Adock Range station came into being.
Each Adcock range station had four 130-foot-tall towers on the corners of a square layout.
The stations emitted unique morse code signals into each quadrant and at the intersections
of each quadrant, the signals would merge into a steady monotone single.
These radio stations were strategically located around the country, around 200 miles apart,
and situated near larger airports and along well-traveled air routes.
These air routes allowed a pilot to navigate fairly precisely along a narrow path (known
as ‘flying the beam’).
While these towers were effective at helping pilots determine what quadrant they were in,
and therefore their rough location, there was no way of determining just from the morse
code signals whether you were moving toward or away from the towers.
And it wasn’t uncommon for so-called ‘ghost signals’ to bounce off mountains and falsely
lead pilots to their doom.
Starting in the 40’s, as radio technology advanced, people realized you could use two
radio signals emanating from different locations to coordinate your location.
This system was known as LORAN, or long range navigation.
LORAN stations, manned by the Coast Guard, were scattered all over the Pacific and were
the first real high tech tool used in navigational history.
To understand how LORAN worked, imagine you’re flying over the beaches of Honolulu with a
LORAN receiver.
Two stations, one on Guam, the other at San Diego, transmit signals outward at the exact
same moment.
The signal from San Diego will arrive first, followed milliseconds later by the signal
from Guam.
The LORAN receiver measures that time difference and could compute a line that would match
up with the time differences between these two stations.
By doing the same thing with two other stations you would get another line, and the intersection
of those lines, would tell you your position.
The LORAN system was particularly useful, because it reallied much less on a pilot's
ability to correctly use and interpret the tool, as was common with previous technologies
like celestial navigation.
The trouble with LORAN was that the signals were in the HF band and very susceptible to
interference from electrical storms.
So in the midst of a storm, when pilots would need the signal the most, they would be unreadable.
In the 50’s we got the VHF Omnidirectional Radio Range (VOR), and the military’s version
the tactical air navigation system (TACAN).
These are the first pairs of technologies we’ve discussed that are still widely used
today.
These technologies are a bit more complicated than LORAN, but here’s the simple version.
Whereas LORAN sent out a steady signal for triangulation, VOR emitted a modulated signal
which consists of two sine waves which are out of phase.
This phase difference allowed pilots to know their bearing, or the direction the plane
was pointed.
This was the first technology that could tell you both your position and your direction
in one measurement.
And on top of that, because of how the receivers worked, you could tell your position from
only one station, whereas with the LORAN system you’d need a minimum of three stations to
triangulate your position.
TACAN works similarly, except that it is more accurate due to its use of multiple frequencies
to triangulate your position, and is used exclusively by military aircraft.
VOR and TACAN are so similar, they’re often placed on top of each other to make the FAA’s
job easier.
Then, in 1978, the first satellite from the Navstar Global Positioning System was launched.
GPS works similarly to the last few technologies, except again, a bit more advanced and a bit
more precise.
The GPS satellites carry very stable atomic clocks that are synchronized with one another
and with the ground clocks.
And in the same manner, the satellite locations are known with great precision.
Each GPS satellite continuously transmits a radio signal containing the current time
and data about its position.
The time delay between when the satellite transmits a signal and when the receiver receives
it is proportional to the distance from the satellite to the receiver.
By monitoring several satellites and doing some math, you can coordinate your position
anywhere on Earth to within less than 20 feet.
At a minimum, four of the 24 GPS satellites need to be in view of the receiver for it
to compute a precise location.
Today’s technology makes air travel much safer and more efficient, but it’s easy
to see how today's GPS technology is built on the back of decades of advancements in
radio-telemetry.
If you like learning about these aviation technologies, check out this video about clever
engineering tricks that have allowed planes to go from this, to this.
Have a great day, and remember, there is always more to learn.